1. Field of the Invention
The present invention relates to a variable valve timing device that is adaptable for an internal combustion engine and can continuously change open/close timing and a peak lift amount of an intake valve and/or an exhaust valve according to an operating state of an internal combustion engine installed on a motor vehicle.
2. Description of the Related Art
A conventional variable valve timing device of this kind is disclosed in Japanese patent laid-open publication No. (Tokkaihei) 11-107725. This conventional variable valve timing device includes a rocker-arm arranged between a drive cam and a swing cam so that the drive cam can drive the swing cam to be swung, where a position of a swing center of the rocker-arm can be changed by a control cam which swingably supports the swing cam at its swing center.
Another conventional variable timing device of this kind is disclosed in Japanese patent laid-open publication (Translation of PCT Application) No. (Tokkyokohyo) 2004-521234. In this conventional variable valve timing device, lift movement of a valve is controlled via a transmitting element by using a control track provided at a one end portion of a swing lever driven by a camshaft of an engine. The other end portion of the swing lever has a swing center point whose position is changeable by using an adjustment device.
The above known conventional variable valve timing devices, however, encounter a problem in that timing, corresponding to rotational phase of the cam shaft, when a valve-lift amount reaches a peak, hardly varies, although a valve-open range, corresponding to a rotational angle of a cam shaft between a valve-open angle and a valve-close angle, and a peak valve-lift amount can be continuously variable.
This causes delay of valve-open timing when the peak lift amount of the valve is set to be smaller. If the device is adapted for an intake valve, too long period causes between exhaust-valve-close timing and intake-valve-open timing.
In order to remove the above-mentioned problem, a timing adjusting device may be added to the variable valve timing device so as to advance the valve-open timing as the peak lift amount becomes smaller. Such the timing adjustment device is constructed to change a rotational phase between a cam shaft and a sprocket driving the cam shaft for example. Consequently, the peak lift amount and the timing are controlled at the same time, which encounters a problem in that the variable valve timing device with the timing adjustment device becomes complex, increasing its weight and manufacturing costs.
It is, therefore, an object of the present invention to provide a variable valve timing device, adapted for an internal combustion engine, which overcomes the foregoing drawbacks and can widely vary timing of a peak-lift position of a valve according to a peak lift amount of the valve and a change of valve-open region without an additional special timing adjusting device.